Sunday, October 25, 2009

Temperature Logger in Refrigerator

The fun continues with my new temperature logger. After leaving it running for a week in my room, I decided to give it a shot at my refrigerator.Click to enlarge.To say the least, I was awfully surprised by the data once I graphed it. First of all, I expected it to be much more temperature stable than it really is. With a slope that high, it's clear that you really don't want to open the door when the power is out, because it is already rapidly approaching room temperature.

The initial drop is just because I started the logger while it was still in my room, since it had to be plugged into my computer to be reset, so it took about an hour for the breadboard to cool off.

Around minute 850, we got home from grocery shopping, so before then, our fridge was rather barren, and the spike was because we had the door open, and were loading warm food into it.

It surprised me how the temperature started swinging more after it was fully loaded, instead of less. This might be because all of the added food blocking air flow means there is a greater differential between the cooling element and the sensor. Any other theories?

The bizarre temperature spike for the last hour didn't actually happen. With a diode and a voltage regulator between my 8V battery pack and the 5V ICs, that left a very small (<0.5v) margin before the regulator started sagging.

I'm really quite interested in seeing what the difference is between the bottom and top of the fridge, and getting more than a day and a half of data. Luckily, I just happened to have ordered TWO temperature sensors, so the only things preventing me from logging two simultaneous temperatures is the lack of spare hookup wire (left my big spool in Sunnyvale -_-), a dozen lines of C, and a fierce competition between roommates about whether we should be keeping temperature sensors or food in the refrigerator.